Hydrogen generation devices use electricity to produce hydrogen (and oxygen) by electrolysis of water in an electrolyzer. The hydrogen generated is stored for use as a fuel, useable in fuel cells and internal combustion engines. The oxygen is vented to the atmosphere. Electrolyzers may be powered by solar energy. Solar hydrogen generation by a photovoltaic-electrolyzer (PV-electrolyzer) is a renewable and environmentally beneficial energy source. Converting U.S. fuel supplies to renewable energy sources is essential for sustainable transportation, sustainable economic growth, reducing greenhouse gas emissions, and for national energy security by replacing polluting fossil fuels imported from unstable regions overseas.
It is not economical to directly connect solar electricity from photovoltaic arrays (PV arrays) alone to power an electrolyzer and produce exclusively renewable hydrogen fuel, although a direct connection method, with the maximum power point voltage of the PV array matching the electrolyzer operating voltage, would give the highest efficiency conversion of solar energy to hydrogen. This lack of economy arises because solar power from a fixed angle PV system is produced effectively for only about six hours per day on average, leaving 18 hours per day when solar electricity production is too little for hydrogen generation and the electrolyzer can not be used. Thus, the electrolyzer is idle most of the time, which increases the size and cost of electrolyzer required for a desired daily fuel production rate. In addition, the electrolyzer is currently the most expensive part of a hydrogen generator system. Therefore, other solutions are needed to make solar powered electrolytic hydrogen production economically viable.